What do people look for when estimating the age of a cat who is full-grown and not yet obviously elderly? Both of my cats came from a shelter and the shelter's age estimates differed significantly from my vet's estimates. When I asked my vet about that she said it's hard to know and she was going on a gut feeling. And previously I had an experienced vet under-estimate a cat's age by more than five years.
I understand that cats don't develop gray hair like dogs do, and dental condition seems to depend as much on prior cleanings as on age itself. What other clues to age are there and how reliable are they?
Per request in a comment, here are photos:
Cat #1 (at least 6) Cat #2 (estimated at 4-7 years)